In earlier years, natural gas was often a nuisance to producers and was burned as a convenient method of disposal. At that time, it was valued at a manufacturing cost of only a few cents per thousand cubic feet. As prices rose, the accuracy of measurement became more important and represented a potentially significant economic loss at every custody transfer point.
Initially, there were few measurement systems although orifice measurement was adopted by the American Gas Association. Venturi nozzles provided good results but were too expensive and needed calibration which was not available in larger sizes. Turbine meters were also available but it was generally accepted that they lacked the necessary degree of accuracy that would permit them to be trusted. As time passed, still other types of meters were introduced and manufacturers were attempting to establish their claims of accuracy.
During these years, those who were buying and selling natural gas have relied on various types of measuring devices. Calibrated liquid filled thermometers have given way to thermocouples and RTD's, pressure gauges have been replaced by pressure transducers and in addition a multitude of special devices have been utilized including gravitometers, densitometers, moisture analyzers and viscosimiters. During this time, the heating value of natural gas was considered, but the difficulty of measurement precluded its widespread use.
Principally, batch calorimeters were known to be available but continuous measurement was at this time first being proposed by Cutler-Hammer. For instance, continuous measurement is contemplated by Cutler-Hammer U.S. Pat. No. 2,238,606 but, while capable of continuous measurement, this device was never in great demand due primarily to its high cost and, in addition, because it required an air conditioned environment for successful operation. Moreover, the Cutler-Hammer device was a large and complicated machine requiring technically qualified operators, high maintenance costs, and a reference gas for calibration.
Nevertheless, the Cutler-Hammer device was considered a standard in the industry until the development of the gas chromatograph. This device does not measure heating value but, rather, does a quantitative chemical analysis. In this manner, the theoretical heating value can be obtained by taking the sum of the values of the different components of the gas.
Among the advantages of the gas chromatograph is its small size and the fact that it does not require an air conditioned environment. It does, however, require a technically trained operator, a certified reference gas and a carrier gas. While its value is recognized by those in the field, the gas chromatograph is limited in usage by a number of considerations, including cost.
In addition to measuring the heating value of a gas, it would also be desirable to measure the heating value of other heating media. This is true in particular of steam since there are many applications in which steam is used for processing and/or heating. However, there has been no truly accurate and effective way of accomplishing this objective.
In view of the foregoing, it has remained to provide a simple, inexpensive calorimeter for measuring the heating value of a heating medium such as gas or steam. In addition, there has been no such calorimeter that can be operated as a stand-alone device with automatic calibration and data transmission to a central processor which can be used particularly effectively at all points in the chain of custody transfer of natural gas from the gas well to the ultimate user. As a result, these are among the principal objects of the present invention as will be apparent from a consideration of the unique features as described hereinafter.
Moreover, since over 95% of all natural gas is used for heating, it follows that gas composition is of little importance in most instances. Thus, it is desirable to avoid the high cost of the gas chromatograph so long as the heating value of gas can be determined at the same or comparable levels of accuracy. Still further, in contrast to the gas chromatograph, it would be desirable to eliminate the need for instruments such as gravitometers, densitometers, moisture analyzers and viscosimiters.
Still further objects of the present invention are automatic calibration and the ability to measure the heating value of a gas at preselected intervals or continuously.